Patent GB-900026-A (GB)
Title: Gating system
IPC: G01S13/70
Filed: 1958-11-18
Abstract: 900,026. Pulse radar; automatic phasecontrol systems. HOLLANDSE SIGNAALAPPARATEN N.V. Nov. 18, 1958 [Nov. 19, 1957], No. 37063/58. Classes 40 (5) and 40 (7). In an automatic ranging pulse radar in which two contiguous narrow gating pulses of equal duration are automatically maintained symmetrically coincident with an echo pulse the initial coincidence is rapidly established by (1) disconnecting the automatic control and adjusting the gating pulses by a coarse manual control to occur slightly earlier than the echo pulse; (2) lengthening the second gating pulse, switching on the automatic control, and, if necessary, adjusting the gating pulses by a fine manual control so that the lengthened second gating pulse overlaps the echo pulse; and (3) allowing the automatic control to adjust the gating pulses so that the echo pulse overlaps both of the gating pulses and then making the duration of the second gating pulse equal to that of the first gating pulse by manual or automatic means ; normal automatic tracking then ensues. The possibility of lengthening both gating pulses is referred to. To facilitate the manual adjustment a gating pulse deflection strobe marker 113 is produced on a type. A C.R.T. range display 112 by a pulse of duration greater than the combined durations of the two gating pulses and symmetrical with respect thereto. As shown, an output from the transmitter trigger pulse generator 101 is applied to a variable delay circuit 115 (e.g. a monostable flip-flop or sawtooth generator and amplitude comparator) whose output triggers the strobe marker generator 117 giving a marker pulse which is applied to the C.R.T. 112 and through a preset fixed delay circuit to a blocking oscillator 121 producing the first narrow gating pulse which is applied to the first gate 129 and to trigger a second blocking oscillator 124 producing the second narrow gating pulse which is applied to the second gate 130. The time constant of the marker pulse generator 117 is such that the duration of the marker pulse is greater than the combined duration of the two narrow gating pulses and the preset delay is such that the gating pulses are symmetrical with respect to the marker pulse. Echo pulses from the receiver 109 are applied in parallel to the gates 129, 130 and the integrated outputs therefrom are applied to a differential amplifier 137 giving a D.C. error voltage which is integrated at 142 giving a D.C. range voltage which controls the variable delay circuit 115. The automatic control is switched off by closing a switch 136 to short-circuit the input to the differential amplifier 137 and the lengthened second gating pulse is produced by operating a switch 131 to apply H.T. to a monostable flip-flop 127 triggered by the second narrow gating pulse blocking oscillator 124, the outputs from the blocking oscillator 124 and flip-flop 127 being combined so that the resultant pulse has a steep leading edge due to the blocking oscillator pulse component; alternatively the flip-flop 127 may be triggered by the differentiated trailing edge of the first gating pulse from the blocking oscillator 121 or the short and long second gating pulses may be produced by the independent generators which are selectively operative. The output from the flip-flop 127 is also applied to the marker pulse generator 117 to give a lengthened marker pulse. The manual adjustment of the gating pulses is effected by a potentiometer device 140 connected to the input of the integrator 142 and controlled by a hand wheel 141 which has three axial positions corresponding to the three modes of operation described above, the switches 136 and 131 being ganged to the axial movement of the hand wheel 141. Alternatively the switch 131 may be automatically restored to its position as shown in response to a combined output from the gates 129, 130, the actuation of the switch being suitably delayed to allow correct synchronization to occur; the combined outputs from the gates 129, 130 may also be applied to other auxiliary control devices 133. In the second mode of operation, i.e. lengthened second gating pulse. and automatic control, if no echo pulses are received the gating pulses will drift due to the unequal noise outputs from the gates 129, 130 and this is prevented by unbalancing the input to an output from the differential amplifier 137 by means of a switch 239, Fig. 2 (not shown), ganged to the pulse lengthening switch 131; alternatively if the variable delay circuit 115 is controlled by a servomotor, the switch 239 may insert a bias in the control circuit of the motor. Circuit detail of the components 117, 121, 124, 127, 129 and 130 are illustrated in Fig. 2 (not shown).